Cyclic thermostat control



July 6, 1943.

G. D. BowE'R CYCLIC THERMOSTAT CONTROL Filed April 6, 1940 6Sheets-Sheet 1 July-s, 1943. Y G, D, BOWER 2,323,370

CYCLIC THERMOSTAT CONTROL .Filed April 6, 1940 y 6 Sheets-Sheet 3 @i a vt /ao /59 "60 ee 62 y far 155 45 46 /f /Z 04 /5 y J5 /A//E/yro E GEORGED. .Banff/E,

July 6, 1943. G D BQWER 2,323,370

CYCLIG THERMOSTAT CONTROL Filed April 6, 1940 6 Sheets-Sheet 4 ,l2 4 f3//47 ,277 45 z 5 32 5 4a p, 4? 56 ,/70 a7 f- *37 il zw 30 33 3f I M @WJuly 5, 1943- G. D. Bowl-:R ,2,323,370

CYCLIC THERMOSTAT CONTROL Filed April 6, 1940 6 Sheets-Sheet 5 A' y 5 /fff-f A rrorA/E/ July 6, 1943. G. D. BowER CYCLIC THERMOSTAT CONTROL 6Sheets-Sheet e Filed April 6, 1940 GEO/EGE 0 en/ER,

/ VEA/TOE Patented July 6, 1943 CYCLIC THERMOSTAT CONTROL George D.Bower, St. Louis, Mo., assignor to Automatic Control Corporation, St.Louis, Mo., a corporation of Delaware Application April 6, 1940, SerialNo. 328,177

(Cl. s-'28) Claims.

The present invention relates to'a control for a heat-change 'producingunit and especially one of the heating variety. It has applicability toafurnace control having a. feed unit, such as a' fected by operation orfailure of the heat-change means; and a stack switch operated by thesaid device. The unit includes also a control motor, which motor rotatesa series of cams, certain of which control and determine thecharacteristics of a cycle of operation for the control motor, andcertain'of which, in iixed relationship to the previous ones, controlthe burner motor and ignition. There is also a manual reset switch'bymeans of which the cycle may be restarted in the event of its failureafter having been previously started.

Among the objects of the invention are the provision of a rate ofheat-change device and a cyclic control under control thereof for theactuation of the heat-change producing unit; a con@ trol for the unitthat gives a definite starting period, a definite running period, and adefinite inactive off (or scavenging) period; the provision of anindependent denite ignition timing, starting with or before fuel and airsupply.

Further objects include the provision of a control of this type, havinga deiinite starting period, time controlled, with means providing that,if at the end of the starting period proper ignition has not occurred,the control deenergizes everything and must be manually reset forfurther operation'.

Furthermore, it is an object to provide that, if power failure or amefailure follows completion of a starting cycle, the control will cutfuel, air and ignitionmeans but will allow the control motor to go on toits starting point and to a position wherein it will re-institute thecycle if there is a demand at the space theremostat.

A further object is the combination with a control of this type forstarting and operating a heat-change producing device, of a deviceresponsive to rate of change of heat to shut off op eration of the fuelsupply upon sharp and abnormal heat changes, but not to cut it oi uponnormal regulatory changes, and particularly with said cut-oi occurringquickly.

It is a further object of the invention to provide such a controlapplicableto any conmbustive type of .heater including stokers, oilburners, and the like.

It is a further object to provide such a control that may be used inconnection with a pilot, for example, such as a gas burner.

A further object is to provide a control unit, whose predetermined cycleis not affected by 'manipulaton of the thermostat.

In the drawings:

Fig. 1 (Sheet l) is a front elevation of the control unt, less itscover, in place on a flue or stack;

Fig. 2 is a side elevation, partly in section, of the unit of Fig. 1,taken on the line 2 2 of Fig. 1;

Fig. 3 is a plan view of the unit with the casing y Fig. 5 is a sideelevation, taken from the right i of Fig. 4, with the casing partly insection;

Fig. 6 (Sheet 2) is a mainly medial, vertical broken section taken onthe line 6 6 of Fig. 4;

Fig. 'I (Sheet 3) is a horizontal upper `section taken on the line 1 1of Fig. 4 through both cam axes;

Fig. 8 is a mainly medial, partly broken, horizontal section on the line8 8 of Fig. 4 through the main axis of the stack switch;

Fig. 9 (Sheet 4) is substantially a rear elevation of the control unitwith the casing in section, taken on the line 9 9 of Fig. 5;

Fig. l0 is a vertical section viewed from the front of the control,taken on the line I0 I0 of Fig. 3; y

Fig. 11 is a vertical section through the stack switch, taken on theline Il ll at the upper right middle of Fig. 8 and showing the mountingof the secondary switch blade;

Fig. 12 is a vertical section on the rrline I2 I2 at the right of Fig.8, showing the contact mountings for both the primary and secondaryswitches of the stack switch device;

Fig. 13 is a vertical section taken on the line I3 I3 at the far rightof Fig. 8;

Fig. 14 (Sheet 5) is a`vertical section on the line Ill-I4 transverselyacross the middle of Fig. 8, showing in particular the* switch lever ofthe stack control;

Fig. 15 isa vertical section on the line |5 |5 of Fig. 3, showing themain timing switch and cam;

Fig. 16 is a vertical section on the line |6 |6 of Fig. 3, showing inparticular the cycle-starting switch and cam; and the intermediateholding circuit switch and cam, which cam is superposed over the oneshown in Fig; 15;

Fig. 17 (Sheet 2) shows the primary lever of the stack switch;

Fig. 18 (Sheet 2) shows the contact bar of the primary stack switch;

Fig, 19 (Sheet 5) is an axial section through the heat-change responsiveunit of the stack switch;

Fig. 20 is a similar section through a modified heat-change responsiveunit for the stack switch;

Fig. 21 (Sheet 6) is a -cyclic diagram of the operation of the control;and,

Fig. 22 is a wiring diagram.

In the exemplication to be described, this control unit is shown appliedto an oil-burning furnace which has an ignition means such as a sparkplug, and has what is here designated a burner motor and which isintended to designate that unit controlling supply of fuel and air tothe furnace.

The control unit includes a casing, from the back of which projects aheat-change responsive device, called here by the trade-nameThermutator, and distinguished from the usual thermostat in that it isoperated in response to heat changes applied above a given minimum rate,and regardless of the starting temperature. The device is mounted withthe thermal unit projecting into some part of the furnace that isquickly responsive to heat of the burner and to a change in that heatproduced, such as would occur when the burner cuts on or off.

As here shown (Figs. 1 and 2), the control box is mounted on a flue 3|and has the thermal element generally designated 32 projecting into theflue. f

The box has a U-shaped bracket with a back 33, from which extend a top34 and a bottom 35. A forward panel board 36 of insulating material issupported in spaced relation to the back` 33 by four posts 31 secured tothe back plate, and with screws 38 passing through the board 36 and intothe posts 31. 'Ihe board 36 extends downwardly from the top 34 butterminates above the bottom 35. A U-shaped casing having a bottom 39 andsides 40 and 4| cooperates with the bracket and the panel 36 to form anenclosure. It has a flange around its front portion, bent over the board36. The casing 39 has flanges 42 at its upper end adjacent the ttop wall34. Screws 43 hold the anges 42 and hence the casing to the top wall 34.

The Thermutator The stack control includes a domed member 45 extendingfrom the back wall 33 and held thereto by four screws 46. An opening 4lis provided through the apex of the member 45, and through it extends atube 48 having a collar 49 thereon limiting the outward movement of thetube through the hole 41. Within the tube 48 is a second tube 58. Thistube, at its outer end, abuts a concave `cap 5I secured to the outer endof the tube 48, enclosing the same.

v An alternative to the cap 5l is shown in Fig. 20, wherein the innertube 510 is made integral with the tube 48 at the outer end, as bywelding. This produces a joint of greater heat conductivity rate thanthat of Fig. 19.

The thermutator is here a device operable in response to heat changesproduced at at least a predetermined rate. Hence, it may be described asresponsive to rate of heat change, upwardly or downwardly. Its operationis independent of ambient temperatures, so that it will operate uponheat change at a suicient rate from any starting or initial temperature.It is independent of slower temperature increases and decreases, such asthe regulations imposed by controls now wellknown, since such changesare at rates too slow to cause the thermutator to shift the switch.

'Ihe Thermutator consists of two members, preferably tubes, securedtogether adjacent one end, one within the other, and with the innermember attached at its free end to a cold reservoir such as the switch.The outer tube is subjected through the major part of its length to theheat of the burner, as by being located in the stack or bonnet of thefurnace, so that it will quickly receive changes in heat produced, andwill be supplied with a relatively infinite source of supply of heat,whereby it will not be reduced in temperatureby any substantial degreebecause of the discharge of heat into the inner tube.

The inner tube receives a substantial, if not major, part of its heat byconduction from the outer, through their' junction. Hence, the attachedend of this tube may be about the same temperature as the outer tube;and the heat from the outer end flows inwardly and ultimately into thecold reservoir, or casing. The inner end of the tube is thus much coolerthan the outer, and the intermediate portions are at intermediatetemperatures, Varied somewhat by other factors, such as radiation, etc.However, since the outer tube is at one high temperature for a largepart of its length-a much larger part than the inner tube-called itsimmersion depth, it can readily be seen that the outer tube under such-circumstances will have a greater total expansion than the inner, andthe inner end of the inner tube will be displaced.

After a short interval of the application of heat to the outer tube, theflow of heat to the inner tube will cause it to expand, and it willagain approach the length of the outer, and reduce the difference intheir rtwo lengths. The time required for this to occur may becontrolled by varying the heat conductivity of the joint between the twotubes, and the conductivity of the path of heat flow whereby thetemperature of the inner tube is raised. Increasing the resistance tothis fiow of heat slows down the rate at which the inner tube followsexpansion and contraction of the outer. Increasing of the resistance toflow of heat from the end of the inner tube to the cold reservoirreduces the length of time required for the inner tube to followexpansions of the outer, and increases the length of time required forthe inner tube to follow contractions of the outer tube, but the latteris ordinarily so slight as not to require consideration.

Since the inner tube is secured to the cold reservoir at one end, itwill never return to its starting length so long as the outer tube is ata different temperature. Whereas the outer tube is subjected to aninfinite heat reservoir so that it does not lose length by the heattransmitted to the inner (and the heat lost from the outer tube to thecasing may be disregarded here), the inner tube constantly loses heat tothe cold reservoir, owing to the fact that the receptivity of the coldreservoir is large relative to the conductivity of the connectionbetween the two tubes. This constant heatloss of the inner tube preventsits ever having heat gain suflicient to have the same length as theouter tube at a temperature above that of the cold reservoir-whichusually is somewhat above room temperature.

In recapitulation, at the start, both tubes are at rest temperature, andof the same length. (Of course, they need not be of identical length,

.and the term same is meant in its broad sense v66 in the to mean theirrelative lengths at the start.) The switch is in its iirst position.Upon sudden application of heat to the outer tube, it will rapidlylengthen, displacing the inner end of the substantially unaffected innertube to shift the switch to second position. After an interval of lag,the inner tube will expand, approaching the outer, but never reachingit, and the switch remains in second position.

Should any variations in the heat produced by the burner occur, as inaccordance with normal regulation, a relatively slow change oftemperature may occur. In such case, the change in temperatures of theinner and outer tubes will occur closely enough together to preventdisplacement of the inner end of the inner tube enough to shift theswitch. l

When there subsequently occurs a sharp reduction of temperature aboutthe outer tube, such as when the burner is cut off, it.will cool rapidlyand contract. Owing to the resistance of the joint between the tubes,the ilow of heat from the inner stud against rotation, while permittingaxial displacement.

to the outer will be slow ..and the reduction in length of the innertube will lag that of the outer. This will cause an exaggerated andrapid displacement of the free end of the inner tube to return theswitch to starting position promptly after the burner stopsagainregardless of the temperature of the thermutator when the action begins.When the inner tube contracts, in due course, the two tubes willapproach the Vsame length determined by the new temperature. If that newtemperature be the cold reservoir temperature, the tubes will attain'thesame length. If it be above the cold reservoir temperature, the innertube will always be somewhat shorter than the outer, but not enough tocause shifting of the switch.

The rate of heat transfer between the tubes is only relatively slow,since actually the inner tube may attain its maximum heat from the outerin a few seconds. However, the reaching of max` imum differential occurseven more quickly,- and actuates the switch. The rate of heat transferis thus suiiicient to enable the two tubes to move together closelyenough to avoid shifting the switch upon regulations of the burner, butinsuiiicient to prevent shifting when the burner changes suddenly. Theproper conductivity is determined by the thickness of the tubes andother factors.

Stack switch Relative movement by expansion between the tubes 48 and 50Acauses actuation of the stack switch, generally designated 52. Thisswitch is preferably attached as a unit to the back wall 33. It includesa channel-shaped casing having a back wall 55 and sidewalls 56 and 51.The screws 46 pass through the wall 55 and secure the switch to the backwall 33 of the control.

The front section of the switch is in two parts. One part consists of aplate 58 attached across the walls 56 and 51 as by bradding 59. Thismember 58 has a bracket 60 on the inner end thereof bent as shown inFig. 8 to receive-screws 69 that pass through the front board 36 of thecontrol.

The other part of the front ofthe switch includes an insulating plate 6|secured across the rest of the front edges of the walls 56 and 51.

A stud 62 has a flange 63 thereon against which thevtube abuts, therebeing a boss 64 to hold the tube from slipping away from the stud. A

pin A| passes through the stud and rides in slots walls 56 and 51,whereby to hold the A washer 61 surrounds the stud and abuts againstlthe back wall 55. A conical coil spring 68 is compressed between thecollar 63 and the washer 61, and urges the stud 62 outwardly7 toward theback of the instrument.

The inner part of the stud 62 is reduced in size to provide a shoulderagainst which rests a washer 10. The stud is threaded to receive anadjustment cap 12' having a kerf 13 accessible through a hole 14 in thefront board 36. The cap passes through and is guidedby an opening15 inthe plate 58.

A sleeve 16 surrounds the stud and has a shoulder between which and thewasher lil Ais disposed a conical compression spring 11. Aself-centering washer 18 engages over the shoulder of the sleeve 16 andit. in turn, is engaged by contact depressions 19 on a primary lever 80.The primary lever is mounted on a pivot pin 8| supported in the Walls 56and 51.

The primary lever has its outer end in contact with a secondary lever 84pivoted on knife-edge bearings 85 formed in the walls 56 and 51. A coilspring 86 is attached to a projection on the secondary lever and to a alug 81 struck out from the plate 58, the spring 86 urging the secondarylever in a direction to contact the primary lever 80.

Th'e secondary lever has a mid-section formed of insulating material andhaving an opening suounding the stud, (see 14). At its outer end, thesecondary lever has an H-shaped double armature 90 (Figs. 13 and 14),the legs of which are on opposite sidesvcf and span the poles 9| of amagnet unit, these poles being embedded within a mass 82 attached to andinsulated from the back member 55. Spark breaking projections 83 extendinwardly from the mass 92, they being oppositely magnetically polarized.For their action, reference is made to application Serial No. 224 838 ofClaude M. Garner, iilcd August 15, 1938.

Adjacent its outer end, the secondary lever has a stop 65 that limitsits travel toward the back plate by contact with the mass 82. A contactplate 96 (Fig. 18) has a pin 81 extending therefrom and passing throughthe secondary lever. The contact plate also has a fork 98 astride themember 95, and a prong 99 within a slot |00 (Fig. 13), by means of whichthe contact plate has a limited movement away from and toward thesecondary lever. A leaf spring |0| is secured to the secondary lever.and acts against the pin 91 to urge the contact plate away from thesecondary lever.

The contact plate ends span two contacts |03 and |04 (Fig. 13) mountedupon angular (see Fig. 8) conducting brackets |05 and |06. respectively.attached to the pla-te 6|. Terminals |01 and |08, respectively, extendthrough the plate 6| for the two contacts |03 and |04.

An adjusting screw |02 (Fig. 8) is threaded into the plate 6| andsecured by a lock nut to limit the movement of the secondary levertoward the frcnt of the switch.

The foregoing contacts form the main switch portionin that, las will beseen, they control the main or highvoltage circuit. There is, however,an additional swtch operated by the secondary lever within the secondaryciscuit of the control.

In Figs. 8, 1l and 12 it is seen that there are two spacer posts |!0attached to the seccndary lever. bridge member spans the two posts tothe plate-6| and having its terminal I2| extending to the front of theplate.

When the secondary lever closes the main switch contacts |03 and |04, italso closes the switch blade H2 with the contact H5. When the mainswitch is open, the contact H3 closes with the contact H6. As isevident, the action of the secondary lever occurs with a snap in bothdirections as the two armatures approach the magnetic poles 9|.

` Reset switch There is areset switch generally indicated at |21 (Figs.6, 8 and `9) secured to the front board 36- It includes a spring blade|28 attached in an insulating block |29 to the panel board 36 and havingan. electric terminal |30 (Fig. 9) projecting from one side thereof. Thespring blade has a double contact |3| on its free end. The contact |3Iis normally in touch with a fixed contact |32 ona short bracket |33,attached to the front board 36 and having a terminal |34 at its otherend. Opposite the contact |32 is a second.contact |35 attached to abracket |36 likewise secured to the front board 36 and having a terminalportion |31 thereon.

A push `button member, generally indicated at |40, projects from thefront board 36 and through the front housing. A spring |4| surrounds areduced portion of this push button |40 and urges it outwardly towardthe front of the instrument. A further reduced portion |42 passesthrough the board 38 and has a collar |43 therearound to prevent itsremoval. The push button may be pressed toward the back of theinstrument until the shoulder |44 strikes the board 36, at which time itwill have contacted the spring blade |28 to displace the contact |3|away from the contact |32 and against the contact |35.

Control motor and cams 'I'here is a control or timing motor |41 securedto the board 36 and operating through suitable gear reduction mechanism,generally indicated at |48, two timing shafts |50 and |5I. The shaft I50 is designed to make twelve revolutions to one of the shaft |I.Normally, the( shaft |50 rotates one time a minute. Both shafts. projectoutwardly in front of the board 36 and have cams thereon.

On the shaft |50 is mounted `a cluster of cams I indicated at |52 whichincludes a hub member |53 secured by a set screw |54 to a. fiat on theshaft. The hub member |53 has a forwardly Vprojecting portion |55 onwhich are mounted two cams |56 and |51 held properly away from eachother by suitable spacer members. A pin |58 fixes the relationship ofthese cams. A screw |59, cooperating with a washer |60 is threaded intothe portion |55 to hold the cam elements removably onto the hub portion|55.

The cam |56 includes a single lobe |62 "of approximately 30 angularextent (Fig. 16). The cam |51 has a single notch |63 of approximately 18angulary extent (Fig. 4)

On the shaft |5| is a hub member |65 secured by a set screw |66 andhaving a projecting portion |61. About the projecting portion |61 arethree cams |68, |69 and |10, all held in spaced relation by suitablespacers and secured to the hub member by a screew I1| and a washer |12.A pin |13 xes the angular relationship of these three cams.

The cam |68 (Fig. 15) has a notch I 14 of approximately 621/2 angularextent. It also has a lobe of approximately 27 angular extent. The cam I69 (Fig. 16) has a lobe |16 of approximately angular extent. The cam |10(Fig. 4) has a deep notch |11 and a shallow notch |18. 'I'he notch |11is of approximately 15 angular y extent, and the notch |18 ofapproximately 171/2 the cam shaft rotates once a minute.

angular extent.

The cam switches a spring blade having a contact I 9|, a terminal |92and a cam followei` arm |93, adapted` to be engaged by the cam lobe |62which causes movement of the blade |90 to bring the contacts .|9| and|88 together. This arrangement is such .as to cause the switch |85 to beclosed for approximately ve seconds out of each minute if This may beseen by reference to Fig. 21.

There is a second switch |95 (Figs. 4 'and 22) 3 likewise secured tothebracket |86 on the board 36. It has a spring blade |96 (second in orderreading upwardly in Fig. 4) having a contact |91 L and a terminal.|98 atits other end; and a second spring blade (fourth in order, Fig. 4) |99having a contact 200, a. terminal 20| and a cam follower arm 202 thatengages the cam |51 and is disposed into the notch |63 .for an intervalof 'approximately three seconds. Normally, the switch |95 is closed andit is, therefore, open for only this short interval. (Compare Fig. 21).

The inner cam |68 on the shaft |5| operates a multiple switch ,205. Thisswitch includes several blades separated by insulators and attached tothe board 36 by a bracket 206. There is a blade 201 having a contact-208and a terminal 209; a blade 2|0 having a double contact 2H and aterminal 2I2; a blade 2|3 having a double contact 2|4 and a terminal2|5; and there. is a blade 2| 8 having a contact 2|1, a terminal 2I8,and a cam follower arm 2|9 that engages with the cam |68 (Fig. 15)

Normally, the cam 68 is in the position shown,

such that the blades 2| 6 and 2| 3 are together closing contacts 2|1 and2|4. vThese two contacts are designated as part a of switch 205. Whenthe cam rotates so that the follower 2|9 slips into the notch |14, theswitch will open al- Fig. 22; and a short interval thereafter there willbe additional displacement closing the contacts 2H and 208, designatedpart c of switch 205, shown on Fig. 22. Approximately. ftyl'secondsbetween d and e in Fig. 21.

later the cam follower 2 |9 will leave the lobe |15 which will openparts b and c, but will leave part A a closed which latter will remainclosed until the expiration of approximately ten minutes from the startof the cycling, as shown on Fig. 21.

There is a switch 225 (Fig. 16) consisting of a pair of spring bladessecured by a bracket 226 to the board 36. There is a switch blade 221having a contact 228 and a terminal 229. Duly insulated therefrom thereis a second switch blade 230 having a contact 23|, a terminal 232 and-acam follower arm 233 that engages the cam |69. The switch v225 isnormally open and is closed when the cam lobe |16 engages the arm 233,to hold Y the switch closedl for an interval of approximately fortyseconds as shown in Fig. 21.

There is a double switch 235 (Fig. 4) that is l also attached by thebracket 22s to the board ss. The switch 235 has a blade 236 (seconddown, Fig. 4) having a contact 231 and a terminal 238.

The switch also includes a blade 239 (third down,

Fig 4) that is part of the same piece of material as is the'blade 230 ofthe switch 225. The blade 239, therefore, does not need an additionalterminal. It does have a two-way contact 240 and a cam follower arm 24|that engages with the.

cam |10. There is a third blade 242 (fourth down, Fig. 4) that has acontact 243 and a terminal 244.

Normally this switch is positioned by the cam tacts 231 and 240,designated part d of switch 235, shown in Fig. 22; However, when thenotch |11 reaches the arm 24|, the arm drops, opening the contacts 240and 231 and closing the contact 240 with the contact 243, the latterbeing designated on Fig. 22 as part e of switch 235. This last remainsclosed for an interval of approximately thirty seconds, as indicated at235e in Fig. 2l. At the end of this interval the cam follower arm 24|ridesinto the shallower notch |18 in which the contact 240 is free ofboth the contacts 231 and 243,so that this switch remains entirely openfor an interval of approximately thirty-five seconds, as is indicated bythe gap notch |18 the arm 24| again moves outwardly and closes the partd, as indicated in Fig. 2l.

Connections in the control The mechanism is provided' with four mainhigh voltage terminals 250, 25|, 252 and 253 for the high voltageconnections. These terminals At the end of the w .V |10 acting upon thearm 24| to close the con' The foregoing completes the main or highvoltage circuits, which are shown in heavy lines.

The secondary or low voltage circuits originate in the secondary 269 ofthe transformer 256, and they all are concerned with the operation ofthe control or timing motor |41, which, therefore, is in series with allof them. From this secondary 269, a lead 210 extends to the clock motor|41. From the other side of the clock motor, a lead 21| extends to'ajunction 212. From the point 212, it branches in a line 213 extendingvthrough a hole 214 to the terminal |98 of th switch |95.

From the point 212, the other branch 215 rextends through a hole 211 tothe terminal 232 vthe switch blade 236.

From the switch 225,'at the terminal 229 of the blade 2,21, a lead 282extends through the hole 211 to the terminal |31 of the switch |21.

From this terminal, a lead 283 also extends to v the terminal ||8 of thestack switch.

From the terminal |34 of the switch |21, the

' flexible lead ||4 extends to the switch blade ||2 receive connectionson both the inside and outside of the board 36. There are alsothermostat terminals 254 and 255 of like character, but `which are lowvoltage connections.

Power lines L from a suitable source are con-- nected to the front sideof the terminals 250 and 25|. A vtransformer-256 has a main lead 251connected to the backside of the terminal 250, and a lead 258 connectedto the terminal 25|. To the terminal 250 there is also attached a lead259 that passes through a hole 260 in the board 36 and is attached tothe terminal 2|8 of the blade 2|6. From the terminal 2|5 of the blade2|3 there extends a lead 26| through the hole 260 to the terminal |01 ofthe bonnet switch. From the terminal |08 of the stack switch a lea 262extends to the main Iterminal 252.

Returning the switch 205, from the terminal 2|2 of the blade 2|0, a lead263 extends through the hole 260 to the main terminal 253; and similarlyfrom the terminal 209 of the blade 201 a lead 264 extends to the mainterminal 252.

of the secondary stack switch.

From the terminal |2I of the stack switch, a

lead 286 extends tothe thermostat terminal 255.

From the other thermostat terminal 254, a lead4 290 extends through thehole 214 to the terminal |92 (Fig. 16) of the blade |90 of the switch|85.

From the other terminal V|89 of the blade |81 oi' this switch, a lead29| extends through the hole 214 through the hole 211 to the terminal244 `of the blade 242 of the switch 235. The external connectionsinclude in the main circuit a burner motor, generally indicated at 295,connected by leads 296 and 291 with the main terminals 25| and 252,respectively. 'I'he external connections also include an ignition device298 connected by leads 299 and 300 with the main terminals 25| and 253,respectively.

In the secondary circuit, the external connections include a roomthermostat30|adapted to close its contacts 302 and 303. A lead 304connects the contact 302 with the terminal 254, and

' the lead 305 connects the contact 303 with the terminal 255.i

The operation of the device is as follows:

At the start it will be assumed that the cam |56 is in position to holdthe switch |85 closed. At the same time, the cam |51 is in position tohold the switch |95 open by engagement of the fol1ower'202 in the camnotch |63. The cam |68 is positioned to maintain switch 205 completelyopen by engagement of the cam follower 2|9 in notch |14. The cam |69 isin position to hold the switch 225 open and the cam |10 is 'in posi'-tion tov close switch 235e'by engagement of the cam follower 24| in thedeep notch |11. The stack switch is open, except at ||6, which insuresthat the high voltage circuit is open.

Thus far, the circuit is merely ready to start. Should the room cool andact upon the thermostat 30| to close contacts 302 and 303, a circuitwill be completed in the secondary. Starting terminal 254, lead 290,terminal |92, switch |85, terminal |89, lead 29|, terminal 244, switch235e, terminal 232, lead 215, junction 212, lead 21|, control motor |41,lead 210, secondary 269, lead 218, reset switch terminal |30, lade |28,contact |3|, contact |32, terminal |34, lead ||4, blade ||2, contact||3, contact ||6, terminal |2|, lead 286, terminal 255, lead 305, and`Lcontact 303.

With the closure of this circuit, the timing motor |41 begins tooperate. In so doing, it first causes the cam |51 to eject the camfollower 202 from the notch |63 and close the switch |95. In accordancewith the desirable order of Fig. 21, this occurs three seconds after theinitiation of' the cycle. It provides a holding circuit for the motor|41. The previously described circuit remains unchanged, but the holdingcircuit to the motor |41 is closed as follows, beginning with theterminal of the switch |95: terminal 20 lead 219, terminal |30 of thereset switch |21, lead 218, secondary 269, lead 210, motor |41, lead21|, junction 212, lead 213 and terminal |98. It will be seen thatclosing of this holding circuit insures that (absent power failure) themotor |41 will run until the notch |63 again opens the switch |95, whichwill not occur until the end of sixty seconds after institution of thecycle, as appears in Fig. 21. Thus, even though five seconds after thestart, the cam |56 opens thenswitch |85, or even though thirty secondsafter institution of the cycle the cam |10 opens the switch 235, or eventhough the thermostat 30| .should open, the circuit will be held untiltheend of this starting phaseinterval, by the Switch |95.

Five seconds after institution of the cycle, the motor |41 will not onlyhave opened the switch |85, but will also have rotated the cam |68 sotha* its cam lobe |15 has begun to lift the follower arm 2|9 of theswitch 205 to an extent sufficient to close the switch 2050,. 'I'hispartially closes a high voltage circuit'between the main terminals 250and 25| as follows: terminal 250, lead 259, terminal 2|8, switch 2050terminal 2|5, lead 26|, terminal |01 of the stack switch and con-'- tact|03 of the stack switch. This switch is in the cold position and so thiscircuit is broken at the point |03. However, a second later, by virtueof continued rotation of the motor |41, the switch 205D is closed bybringing together contacts 2|4 and 2| This closes high voltage circuitas follows: terminal 250, lead 259, terminal 2|8 of the switch 205,switches 205a and 2051i, terminal 2|2, lead 263, main terminal 253,external lead 300, ignition device 298 and lead 299 and the mainterminal 25|.

Sparking of the ignition device then begins within the furnace. 'At itsinception, however, there is no fuel supplied, since the motor 295hasnot been put in circuit.

One second later, continued rotation of the cam |68 closes theswitchg205c and brings together the contacts 2| and 208. This closes thecircuit that short circuits the stack switch and So puts the burnermotor 295 in circuit as follows: main terminal 250, lead 259, terminal2|8 of switch 205, switches zosa, 205e, and 205e, terminan 209, lead264, main terminal 252, lead 291, motor 295, lead 296, and main terminal25|. The burner motor, therefore, starts and sends combustible thepreviously or concurrently started ignition mechanism 298. Both theburner motor and the ignition mechanism are held in operation for adefinite interval of time, such as one minute, by

` fuel mixture into the furnace, which is ignited by `at the contact302, the circuit will be: lead 304,

the cam lobe |15, its cam |68 being rotated by the control motor |41which is held in circuit until the end of a full minute by the holdingcam |51.

The foregoing is the starting phase of the cycle.

As previously observed, the switch 235e is lopened at the end of thirtyseconds from the beginning of the cycle. No change is produced by this,however, as the holding cam |51 continues the motor |41 through theswitch |95 until the end of a minute.

In normal operation, ignition will occur and the furnace willimmediately supply heat to the thermutator 32. This heat will move as aWave against the thermutator fast enough to cause shifting of the stackswitch to the second position, shown in Fig. 8, wherein th blade 84closes together the contacts |03 and |04 and the blade ||2 closes withthe contact ||5. Of course, this occurs only if ignition takes place.Its effect is to open the room thermostat circuit again, at I6, butalso, by closing with ||5, to cock the circuit of the control motorthrough the switch 225, so that it can be held upon closure of thatswitch,

as will appear hereafter. It also closes the main circuit through theswitch 205a as follows: main terminal 250, lead 259, terminal 2|8,switch 205a, terminal 2|5 thereof, lead 26|, terminal |01 of the stackswitch, contact |03, blade 84, contact |04, terminal |08, lead 262,terminal 252, lead 291, motor 295 and lead 296 to terminal 25|. Thecircuit is set up then to hold the burner motor in operation after theshort circuit through blade 201 of switch 205 is broken, provided ofcourse the thermutator 32 is not changed.

As forecast, there is set up by this action of the stack switch, anadditional intermediate holding circuit for the timing motor |41, whichholding circuit is thereby dependent upon there being effectiveignition. This circuit, beginning at the motor |41 is as follows: lead21|, point 212, lead 215, (branch 216) terminal 232 of the switch 225(which switch is closed beginning 40 seconds after initiation of thecycle, as shown in Fig. 21) terminal 229, lead 282, terminal |31 of thereset switch, lead 283, terminal I8 of the stack switch, contact ||5,blade ||2, lead ||4, terminal |34 of the reset switch, contact |32,contact |3I, blade |28, terminal |30, lead 218, secondary 269, and lead210 to the motor |41. This holding circuit for the motor |41 is closedat the switch 225 only after passage of forty seconds or ten secondsafter switch 235e has opened, which gives time for the ignition to beeffective. If the ignition is effective on the stack switch at any timeprior to the expiration of the minute during which the holding cam |51keeps switch |95 closed, the motor |41 will be kept in operation by theswitch 225 and its circuit for an'interval until eighty seconds afterstart of thecycle. If the ignition is ineffective at the end of theminute, the circuit through the switch 225 will be brokenat |5, and thewhole mechanism will stop upon opening yof the switch |95. Thus theswitch 225 is an intermediate holding circuit switch, dependent uponignition, to bridge between the starting and running phases of thecycle.

Continuing normal operation and assuming effective combustion, theswitch 225 will close and it will keep the motor |41 running. At the endof sixty seconds, the switch |95 will open but the switch |85 will beclosed again. The latter is immaterial, since its circuit is open atseveral points. Also at the end of about a minute, the switches 205D and205e open. Thus, at the end promptly upon temperature changes.

of a minute the short circuit to the burner motor around the stackswitch is broken, and the circuit for the ignition device is open. Themain circuit for the burner motor continues through the hot stackswitch. As shown in Fig. 21, its circuit is held by the cam |68 for aninterval of ten minutes, 'but is at all times dependent upon themaintenance of heat in the burner and is opened in the event the firefails, and also in case power fails.

After the expiration of sixty-five seconds, the cam follower 24| ridesout of the shallow notch |18 and onto the body of the cam |10. Thiscloses the-switch 235d. This closes a running phase switch |95 breaksafter the first minute of the cycle. f 1

AlmOrmal operations phase carries on only if the starting effectivelyondary 269, and' lead 210 to the motor |41. If

this holding circuit closes, it continues for almost the remainder ofthe full twelve minute cycle but terminates about ten seconds short ofthis limit as appears in Fig. 21. It will be remembered that, since itis dependent upon operation of the intermediate holding switch 225, itcan never close unless ignition has taken place, and that once it doesclose, it insures a complete cycling of the running phase of the controlmotor |41. It will further be observed that even though, afterinstitution of this main holding circuit, the burner motor circuit isbroken, the timing motor |41 will continue to operate for the remainderof its cycle, 'returning to starting position.

Furthermore, in normal operation, this means that the burner motor willalways be operated for a period of approximately ten minutes, regardlessof the condition of the room` thermostat. The burner motor, of course,stops when the cam follower 2|9 of switch 205 falls into the `notch |14which it does at the end of ten minutes.

- Thereafter, the cycle continues until the switch 235d opens itsholding circuit, during a scavenging period.

The foregoing is a normal cycle of operation. Continuation of the heaterby recycling is made dependent upon return of the unit to startingposition. At the time the switch 235d opens its holding circuit, theholding circuit through the switch |95 is closed by cam |51, since thefast cams |58 and |51 recycle their switches every minute. When theswitch 235d opens the holding circuit, it closes at 235e in the roomthermostat circuit, but the motor |41 continues under the holdingcircuit of cam |51 until that circuit opens. However, just prior toopeningI of the switch |95, the switch |85 in the thermostat circuit isclosed by the cam |56. When the burner motor stops by opening of theswitch 2050., after ten minutes, the thermutator 32 at once cools toreturn the stack switch to Starting position as heretofore described,regardless of the particular temperature of the tubes at the time theywhich the switch 235d opens.

Recycling can then begin if the room thermostat closes or remainsclosed, as theother switches 85, 235e and 52 are in starting position.

As above described, the thermutator 32 shifts For this reason, ignitionwill cause shifting of the stack switch. to its upper position inFig.'22 almost immediately and in suilicient time to effectuate theintermediate holding circuit through the switch 225 when the startingholding circuit through caused combustion, so that the intermediateholding mechanism could bridge the gap between the two.

If the burner is not ignited during the starting phase (such as by abreakdown of the ignition mechanism), or failed to be effectivethroughout the gap between the phases, (such as by power failure) sothat the stack switch is.

open at the end of the starting phase, the main circuit to the burnermotor, and the secondary circuit through the timing motor are opened atthe end of the starting phase. Thereafter it would be necessary to resetthe unit manually, by depressing the button |43. a circuit through theintermediate holding switch 225 that short circuits the stack switch asfollows: motor |41, lead 21|, point 212, lead 215 (branch 215), terminal232, switch 225, terminal 229, lead 282, terminal |31 of'reset switch|21, contact |35, contact |3'I, blade |28, terminal |30, lead 218,secondary 289, lead 210 to the motor. The button is held down untilswitch 23511 closes the running holding circuit, which will complete thecycle and return it vto starting position.

In the event the flame stops, during the running phase, after closing ofholding switch 235d, there will be a. rapid lowering of the temperatureof the tube 48 and, consequently, rapid shifting of the stack switch toits lower position.

This immediately cuts out the motor 295, but the timing motor |41continues to the end of its room thermostat demands heat.

In the event of power failure during the starting phase, the stackswitch will cool, and upon return of power, the starting phase will takeup where it left off. If the remainder is insufficient toproduce-starting, and heat change to shift the stack switch, theintermediate holding circuit through the switch 225 and the stack switchwill not close, stopping the cycle, and requiring manual reset. If thepower failure occurs during the intermediate holding phase, whichassumes effective starting, the thermal inertia of the thermutator 32may hold the stack switch in hot position for the remainder of the fiveseconds duration of the intermediate phase, and until the runningholding circuit can' cycle out. Otherwise (and the thermutator isnormally responsive in three seconds or less), the switch 225 will open,and manual reset will be necessary.

If power failure occurs during the running phase, the cooling of thethermutator 32 will open the circuit to the burner motor and cut off thesupply of fuel. Subsequent restoration of power cannot restart theburner motor after the starting period, since the ignition'mechanism isinoperative; with the result that the stack switch does not heat andreclose. However,'the restoration of power will cause the timing motorto complete its cycle and be ready for recycling in the event the roomthermostat still calls for heat.

It is apparent that this mechanism could be used where there is a pilot,since this would in- This establishes volve merely lifting the terminal253 out of circuit.

In the foregoing, it will be seen that there is in every cycle adefinite starting time interval, a definite running time intervalfollowed by a definite inactive interval of the burner. There is alwaysan independent ignition actuation operating for a fixed period of timewhich starts with or before the fuel and air supply. Manipulation of thethermostat cannot effect the predetermined operating cycle, because thethermostat is ineffective after a few seconds once the cycle isinitiated.

Likewise there is provided a burner control and a device operative inresponse to rate of heat changes, so that the control is subjected tooperations dependent upon the existence or nonexistence of a supply ofheat, producing heat changes, rather than upon a given amount of heat orvalue of temperature.

What is claimed is:

1. In a mechanism of the kind described, a burner, a fuel supply meanstherefor, an ignition device for the burner, a space thermostat, meansoperable upon shifting of the space thermostat to cause operation of theignition device and the fuel supply means, means to maintain both ofsaid operations for a given rst time interval, means effective a periodafter ending of said first interval for maintaining the supply means inoperation for a given second time interval, and means dependent uponcombustion of the fuel to hold said supply means in operation from thefirst interval to the second.

2. In a mechanism of the kind described, a temperature-change producingmeans, an automatic external control device actuated in response topredetermined external conditions, a starting means to render thetemperature-change means effective, means to sustain the operation ofthe temperature-change means, and a control mechanism adapted to be putinto operation by the automaticexteranal control device, said controlmechanism including means to operate the starting means, means to causeoperation of the first means by the starting means, means to maintainthe first means in operation for a Dredetermined interval afterstarting, and means to prevent its restarting for a second predeterminedperiod after the first interval.

3. In a mechanism of the kind described, a temperature-change producingdevice, means to start the same, means to run the same, means to stopthe same and prevent its running, means coordinating said several meansto cause them to cycle in the order named within a fixed time intervaland then to recycle, and an over-al1 automatic control device adapted todetermine the start of the cycle, said control device being thereafterineffective to stop the same until the' end of a cycle.

4. In a mechanism of the kind described,a burner, a temperature deviceto receive immediately the heat from burning therein, means to supplyfuel to the burner, and timing mechanism including a timing motor, meansto cause starting of the timing motor, first means to maintain the motoroperating during a given starting period, means operated by the timingmotor to cause operation of the fuel supply means, means to maintain thesupply means and the timing motor in operation after the starting periodincluding the timing motor and a circuit therethrough, said circuit alsopassing through the temperature device only when it is hot, and meansoperated by the timing motor to stop the supply means after operationthereof for a predetermined lnterval of time after said starting period.

5. In a mechanism of the kind described, a burner, a fuel supply meanstherefore, an ignition means, a room thermostat, a temperatureresponsivedevice located so as to be shiftable promptly in response to changes intemperature produced by the burner, a'reset switch, and a timingmechanism, said timing mechanism having a motor and a plurality of camswitches operated thereby, a first circuit including in series a firstcam switch, the room thermostat, a second cam switch, thetemperature-change device in cold position, and the reset switch innormal position, and the two cam switches being closed at the start ofthe cycle, the timing motor starting upon closing of the circuit by theroom thermostat, the two cam switches being opened shortly afterstarting of the motor, a second circuit and a third cam switch closed inthe second circuit prior to opening of the first circuit, and beingadapted to hold the timing motor in operation a predetermined periodafter start of the cycle, independently of the rst circuit, a thirdcircuit including the temperature-change device in hot position, and acam switch therein adapted to be closed during the starting period, a.fourth circuit including the ignition means, and a cam switch in thecircuit adapted to be closed during the startingl period, a fifthcircuit including the supply means and independent of thetemperature-change device, the timing motor, during the starting period,causing the fifth and fourth circuits to be closed, and causing its partof the third circuit to be closed, the fth and fourth being subsequentlyopened at the end of the starting period and the third being closed thenif ignition occurs to shift the temperaturechange device to hotposition, a sixth intermediate holding circuit including the timingmotor, the temperature-change device when hot, and the reset switch, andincluding a cam switch closed when the second circuit opens, the camswitch remaining closed for an intermediate pesaid seventh circuit, whenclosed, being held closed at its cam switch for the duration of arunning period, and the third circuit being opened by its cam switch ata predetermined time before end of the running period, the first circuittiming cams being closed at the end of the running period, wherebyrecycling can occur if the room thermostat is closed.

6. In a control system, a burner device, an`

external control device, meansv to cause operation of the burner devicefor a starting period, including the external control device, and meansfor maintaining the burner device in operation for a running period,independent of said external control device, and means independent ofAsaid external control device for` stopping the burner device at the endof said running period.

'1. A method of operating burner devices requiring ignition, comprisingthe steps of starting the device upon temperature demandx continuing itsoperation upon occurrence of ignition, maintaining its operation for ameasured interval after start, and then causing it to stop regardless ofthe temperature demand. g

8. A method of operating burner devices requiring ignition, comprisingthe steps of starting the device upon temperature demand, continuing itsoperation for an ignition interval and maintaining its operation for apredetermined measured running interval after said ignition interval,

and then causing it to perature demand.

9. A method of operating burner devices requiring ignition, comprisingthe steps of starting the device upon temperature demand, continuing itsoperation upon occurrence of ignition, maintaining its operation for ameasured running interval, causing it to stop at the end of saidmeasured running interval, preventing its operation for a scavengingperiod after the running interval, and then recycling it upon further orcontinued temperature demand.

l0. In a control mechanism, a burner device requiring ignition, externalcontrol means, and a cycling device, said cycling device having means tocause starting of the burner device upon operation of the externalcontrol means, and including means dependent upon occurrence of ignitionto maintain the burner device in operation for a measured interval afterthe starting, means to stop the burner device at the end of saidmeasured interval, and means thereafter to return the cycling device toits original condition.

11. In a control mechanism, a burner device requiring ignition, anexternal control means, and a cycling device, said cycling device havingmeans to cause starting of the burner device upon operation of theexternal control means, means dependen-t upon occurrence of ignition tomaintain the burner device in operation for a measured interval afterstarting, meansto stop the burner device at the end of said measuredinterval, means to prevent restart for an additional interval, and meansto return the cycling mechanism to its original condition at the end ofsaid additional interval.

12. In a control mechanism, a burner device requiring ignition, anexternal control means, and a cycling device, said cycling device havingmeans to cause starting of the burner device upon operation of theexternal con-trol device, means to stop the burner device if ignitiondoes not occur, means to continue operation of the burner device for ameasured interval after starting if ignition does occur, and meansthereafter to stop the same.

k13. In a mechanism of the kind described, a burner device requiringignition, a cycling mechanism therefor including a control motor,autostop regardless of temmatic means responsive to changes in physicalconditions to cause said control motor to start,

for a plurality of said cycles to render said rst switch ineiective toclose the circuit after said.

first cycle, a second circuit, with means to close the. second circuitwhen the second switch is open, and mechanism adapted to be operated byeach of said circuits, said mechanism being adapted for control of saidtemperature-change device.

15.'In a mechanism of the kind described, a burner device dependent uponignition, a circuit therefor, switch means in the circuit, a controlmotor for operating said switch means, circuits for the control motorcomprising an instituting circuit to cause starting of the controlmotor, a holding circuit to insure operation of the control motor vfor apredetermined period regardless ofy the instituting circuit, a runningcircuit to hold the control motor in operation for a running periodbeginning after the end of the holding circuit period, and anintermediate circuit dependent upon eiective ignition tov continueoperation of the control motor from the end of the holding circuitperiod to the beginning of the running period, and a circuit controlledby the control motor to hold the burner device in operation during therunning period.

16. In a mechanism of the kind described, a

Y burner device, means including a space thermostat to start said burnerdevice, automatic control mechanism including means to render thethermostat ineffective to stop the device, 'and maintain the device inoperation independently of thethermostat for an interval, and saidautomatic control mechanism including means independent of thethermostat to stop the device.

17. In a mechanism of the kind described, a burner device, a spacethermostat adapted vto operate in response to temperature changescontrolled by the burner device, and control mechanism producing acomplete cycle of operation of the burner device including starting -thehsame, running it for a running interval and stopping it after saidinterval, said control mechanism having means dependent upon the roomthermostat for starting the operation, and means independent of thethermostat for stopping it after said running interval.

18. In a mechanism of the kind described, a burner device, a circuittherefor, a control device including a control motor and switchesoperated thereby, a rst circuit for the control motor, one of theswitches being in the burner device circuit and one being in the controlmotor circuit, and alternate circuits dependent upon ignition of theburner device, one for the control motor and one for the burner device,said conmeans operated by the motor to cause the burner device tooperate, means dependent upon ignition to maintain the burner device inoperation, and means maintaining the control motor in operation at alltimes during operation of the burner device.

14. In a, mechanism oi the kind described, a temperature-change device,a. iirst circuit, a member in said circuitV to be operated upon closurethereof, and control mechanism for the circuit, said control mechanismincluding a rst switch adapted to open and close repeatedly in shortcycles, and a second switch adapted to close during one of said cyclesbut to open thereafter trol motor being adapted to open the rst burnerdevice circuit switch not later than it opens its own first circuitswitch. y

19. In a mechanism of the kind described, a burner device, a controlmotor and a plurality of switches operated thereby a, stack switch, anda space thermostat, circuit means for the control motor adapted to startthe same upon demand by thespace thermostat and to maintain the same inoperation stack switch for a predetermined period of time, and then tostop the same, and circuit means for the burner device operated bycontrol motor switches to start the same, to maintain the same inoperation upon actuation of the stack switch, and to stop the same notlater than the end of the predetermined period of operation of thecontrol motor.

20. In a mechanism of the kind described. a

upon actuation of the burner device, a circuit for the burner device, anexternal control device, a timing control, means starting operation ofthe burner device including the external control, and means to provide arunning period for the device, said means including the timing controlin operation, and including a switch operated by the timing control, inseries with the burner device, whereby the mechanism is dependent onlyupon continued operability of the timing control to prevent unlimitedoperation of the burner device.

21. In a mechanism of the kind described, a burner device, a circuittherefor, a timing control device, means in the timing control device toclose the burner device circuit for a first interval, means to hold thecontrol device in operation for said interval, means to hold the controldevice and burner device in operation after said interval and for asecond interval dependent upon combustion from the burner device, saidcontrol device fand said burner device being rendered inoperative aftersaid rst interval upon non-existence of combustion, means to maintainthe control device in operation for a third interval after said secondinterval regardless of combustion, means dependent upon combustion tomaintain said burner device in operation in said third interval, andmeans to stop the burner device and control device by the end of thethird interval.

22, In a mechanism of the kind described, a burner device, a circuittherefor, a timing control device including a plurality of switchesoperated in timed relation, a space thermostat, a combustion switch,said timing control device switches including two fast switchesoperating in a repeating cycle and other switches operating in a longcycle greater than the repeating cycle, a rst instituting circuitincluding a first fast switch, the thermostat, the combustion switchcold and the timing device, said timing` device being adapted tothereafter close the second fast switch and after such closing to openthe iirst fastswitch, a second circuit for the timing device includingthe second fast switch, said second circuit being held closed for ailrst interval, a third timing device switch closed during said firstinterval, and opened by the end thereof, and a first burner devicecircuit including said third switch, a third timing device circuitincluding a fourth timing devce switch closed for a second interval uponopening of the second fast switch, and the combustion switch hot,whereby upon absence of ignition at the end of said first interval themechanism may stop, a fourth timing device circuit including a iiithtiming device switch closed for a third interval a time later thanopening of the `second circuit, a second burner device circuit includingthe combustion switch hot and a sixth timing device switch closed priorto opening of the first burner device circuit, and, dependent uponcombustion, adapted to maintain the burner device in operation until atime not later than the opening of the fourth timing device circuit, andsaid timing device being adapted to close its part of the institutingcircuit by the time the fourth timing device circuit is opened.

23. In a mechanism of the kind described, a burner device, a timingcontrol device including a plurality of switches operated in timedrelation, a space thermostat, a combustion switch, a first circuit forthe timing device including the thermostat, and the combustion switchcold, a second circuit for the timing device including a timing switch,said second circuit being adapted to shunt the thermostat, a firstburner device circuit including a timing switch adapted to be opened notlater than opening of the second timing device circuit, means to openthe ilrst timing device circuit when said second timing device circuitis opened, a third timing device circuit including the combustion switchhot, and a fourth timing device circuit adapted to be .closed after saidthird circuit has been closed for an interval, said .fourth circuitshunting the combustion switch, a second burner device circuit includingthe combustion switch hot and a timing switch closed before opening ofthe first burner device circuit, and opened not later than opening ofthe fourth timing device circuit, and means to render said first timingswitch opening means inoperative at the end of said fourth timing devicecircuit interval.

24. A mechanism as in claim 23, together with reset means in said thirdtiming device circuit adapted to shunt the combustion switch and startthe timing device.-

25. In a mechanism of the kind described, a. temperature-change device,an automatic external control device adapted to actuate in response topredetermined external conditions, operating means put i-n operationupon actuation of the external control device, said operating meansincluding mechanism adapted to cause operation of the temperature-changedevice for a predetermined interval of operation after closure of saidautomatic external control device, and said operating means includingmechanism adapted to prevent further operation thereof for a secondpredetermined time interval after the iirst.

. GEORGE D. BOWER.

